Phase I Environmental Site Assessment

In the United States, an environmental site assessment is a report prepared for a real estate holding that identifies potential or existing environmental contamination liabilities. The analysis, often called an ESA, typically addresses both the underlying land as well as physical improvements to the property. A proportion of contaminated sites are "brownfield sites." In severe cases, brownfield sites may be added to the National Priorities List where they will be subject to the U.S. Environmental Protection Agency's Superfund program.

The actual sampling of soil, air, groundwater and/or building materials is typically not conducted during a Phase I ESA. The Phase I ESA is generally considered the first step in the process of environmental due diligence. Standards for performing a Phase I site assessment have been promulgated by the US EPA and are based in part on ASTM in Standard E1527-13.

If a site is considered contaminated, a Phase II environmental site assessment may be conducted, ASTM test E1903, a more detailed investigation involving chemical analysis for hazardous substances and/or petroleum hydrocarbons.

As early as the 1970s specific property purchasers in the United States undertook studies resembling current Phase I ESAs, to assess risks of ownership of commercial properties which had a high degree of risk from prior toxic chemical use or disposal. Many times these studies were preparatory to understanding the nature of cleanup costs if the property was being considered for redevelopment or change of land use.

In the United States of America demand increased dramatically for this type of study in the 1980s following judicial decisions related to liability of property owners to effect site cleanup. Interpreting the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), the U.S. courts have held that a buyer, lessor, or lender may be held responsible for remediation of hazardous substance residues, even if a prior owner caused the contamination; performance of a Phase I Environmental Site Assessment, according to the courts’ reasoning, creates a safe harbor, known as the 'Innocent Landowner Defense'.

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